1. Field of the Invention
The present invention relates to a mobile communication apparatus such as a cellular phone, and a position detection method for detecting its position.
2. Description of the Related Art
Conventionally, a method for using radio waves coming from base stations and a method for mounting a GPS (Global Positioning System) receiver to use radio waves coming from GPS satellites have been known as a position detection method for detecting a position of a mobile communication apparatus such as a cellular phone or PDA (Personal Digital Assistants).
In the position detection method for using the radio waves coming from the base stations, the mobile communication apparatus measures each propagation time of the radio waves coming from the plural base stations constructed in a communication area (service area) of a mobile communication network. Then, by converting each the measured propagation time into a propagation distance and applying triangulation to make an analysis, the present position of the mobile communication apparatus is obtained.
In the position detection method for mounting the GPS receiver in the mobile communication apparatus to use the radio waves coming from the GPS satellites, the radio waves coming from the plural GPS satellites are received by the GPS receiver and each propagation time of the incoming radio waves is measured. Then, by converting each the measured propagation time into a propagation distance and applying triangulation to make an analysis, the present position of the mobile communication apparatus is obtained.
However, the conventional position detection method for using the radio waves coming from the base stations is susceptible to multi-path fading. Therefore, there was a problem that a case that the present position of the mobile communication apparatus cannot be obtained with high accuracy occurs.
That is, there is a case that the radio waves emitted from the base stations are reflected by buildings and become a multi-path wave and reach the mobile communication apparatus, and even when propagation time of this multi-path wave is measured and is converted into a propagation distance, the propagation distance does not indicate a linear distance between the base station and the mobile communication apparatus. Because of this, even when the propagation distance obtained from the multi-path wave is applied to the triangulation, there was the problem that the case that the present position of the mobile communication apparatus cannot be obtained with high accuracy occurs.
Particularly, in a place where buildings of a city are crowded, a case that the multi-path wave is received and the propagation distance is measured often occurs, so that it became difficult to improve accuracy of position detection.
In the conventional position detection method for mounting the GPS receiver and performing the detection, there was a problem that power consumption becomes large.
That is, since the power consumption is large in the GPS receiver, when the GPS receiver is mounted in a mobile communication apparatus with a small battery capacity and position detection is performed, operable time of the mobile communication apparatus becomes short and there was a problem that a result that loses excellent portability which the mobile communication apparatus has essentially is caused.
Also, since there is a case that the radio waves from the GPS satellites cannot be received within a shield such as a tunnel or a building, there was a case that a situation in which position detection cannot be performed is caused.
The invention is implemented in view of the conventional problems, and an object of the invention is to provide a mobile communication apparatus capable of detecting a position of the mobile communication apparatus with higher accuracy and a position detection method thereof.
Another object of the invention is to provide a mobile communication apparatus for detecting a position of the mobile communication apparatus with more reliability and a position detection method thereof.
A further object of the invention is to provide a mobile communication apparatus capable of reducing power consumption and a position detection method thereof.
In order to achieve the objects, there are provided a mobile communication apparatus and a position detection method, wherein the present position of the mobile communication apparatus from radio waves coming from base stations and a position measurement error are measured and the position measurement error is compared with a predetermined criterion and the present position of the mobile communication apparatus is measured from radio waves coming from GPS satellites when the position measurement error exceeds the predetermined criterion.
A measurement error of the present position of the mobile communication apparatus measured from the radio waves coming from the GPS satellites is compared with a predetermined criterion and when it is decided that the measurement error of the present position measured from the radio waves coming from the GPS satellites exceeds the predetermined criterion, a new present position is calculated within a range of overlap between the position measurement error of the present position obtained from the radio waves coming from the base stations and the position measurement error of the present position obtained from the radio waves coming from the GPS satellites.
According to such a mobile communication apparatus and a position detection method, the present position of the mobile communication apparatus from radio waves coming from base stations and a position measurement error are first measured and the position measurement error is compared with a predetermined criterion and when the position measurement error does not exceed the predetermined criterion, the present position obtained from the radio waves coming from the base stations is set to a true present position of the mobile communication apparatus. As a result of this, power consumption necessary to make distance measurement and position measurement of the present position of the mobile communication apparatus from the radio waves coming from the GPS satellites is reduced.
Then, when the position measurement error at the time of obtaining the present position of the mobile communication apparatus from the radio waves coming from the base stations exceeds the predetermined criterion, the present position of the mobile communication apparatus is measured from the radio waves coming from the GPS satellites.
Also, when the measurement error of the present position of the mobile communication apparatus measured from the radio waves coming from the GPS satellites exceeds the predetermined criterion, a new present position is calculated within a range of overlap between the position measurement error of the present position obtained from the radio waves coming from the base stations and the position measurement error of the present position obtained from the radio waves coming from the GPS satellites.
When a range of overlap between such position measurement errors is obtained, the overlap range becomes a range indicating the present position with position measurement accuracy higher than that of the present position obtained from the radio waves coming from the base stations and the present position obtained from the radio waves coming from the GPS satellites, and by calculating a new present position within this overlap range, more proper present position of the mobile communication apparatus is obtained.